feat(server): add server manager install script to support rootless docker

[Friend-LGA]

Right now default install flow is using this script

sudo bash -c "$(wget -qO- https://raw.githubusercontent.com/Jigsaw-Code/outline-server/master/src/server_manager/install_scripts/install_server.sh)"

This one doesn't work with Rootless Docker because of 2 reasons:

• --net host flag
• usage of watchtower

This PR adds new script install_server_rootless.sh which maps docker ports directly using -p flag and removes usage of watchtower.

Works with Rootless Docker (tested).

Example usage

bash -c "SHADOWBOX_DIR=$HOME/outline-data $(wget -qO- https://raw.githubusercontent.com/Jigsaw-Code/outline-server/master/src/server_manager/install_scripts/install_server_rootless.sh)"

Notice no sudo is here and custom shadowbox dir.

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